Two cleanups:
* si->cur_comp, si->cur_pg where always calculated after
the call to ore_calc_stripe_info() with the help of
_dev_order(...). But these are already calculated by
ore_calc_stripe_info() and can be just set there.
(This is left over from the time that si->cur_comp, si->cur_pg
were only used by raid code, but now the main loop manages
them anyway even though they are ultimately not used in
none raid code)
* si->cur_comp - For the very last stripe case, was set inside
_ore_add_parity_unit(). This is not clear and will be wrong
for coming raid6 so move this to only caller. Now si->cur_comp
is only manipulated within _prepare_for_striping(), always next
to the manipulation of cur_dev.
Which is much easier to understand and follow.